Process for making a nonwoven fabric having substantially uniform ripples



Dec. 23, 1969 A. H. BASSETT ET AL 3,485,699

' PROCESS FOR MAKING A NONWOVEN FABRIC HAVING SUBSTANTIALLY UNIFORM RIPPLES Filed Jan. 29, 1965 5 Sheets-Sheet l Dec. 23, 1969 A. H. BASSETT E AL 3,485,699

PROCESS FOR MAKING A NONWOVEN FABRIC HAVING SUBSTANTIALLY UNIFGRM RIPPLES Filed Jan. 29, 1965 5 Sheets-Sheet 2 lNVELNTORSI 44 70m A! 545x77 BY (7/4/9455 6. Pzwmm-W C/ ATTQBLNEYV Dec. 23, 1969 A BASSETT ET AL 3,485,699

PROCESS FOR MAKING A NONWOVEN FABRIC HAVING SUBSTANTIALLY UNIFORM RIPPLES Filed Jan. 29, 1965 5 Sheets-Sheet 5 Den 3, 1969 A. H. BASSETT ET 3,485,699

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United States Patent US. Cl. 156-290 4 Claims ABSTRACT OF THE DISCLOSURE A nonwoven fabric having substantially uniform ripples throughout and rendered substantially unaffected by shrinkage at elevated temperatures.

More particularly, the process of the present invention is concerned with so-called nonwoven textile fabrics, i.e., fabrics produced directly from individualized textile fibers without the use of conventional spinning, weaving or knitting operations, and a method for providing a nonwoven fabric having unusual three-dimensional effects which are dimensionally stable in such nonwoven textile fabrics.

US. Patent 3,214,323 to G. D. Russell et al. discloses and claims a new nonwoven fabric characterized by unique buckles or ripples. The present invention resides in a process for making a rippled fabric which includes a mechanism to control the extent of activation of the fibers involved; as well as, a mechanism to insure that the activation is substantially finalized and that no greater than about 2% post activation will result, if in fact more than very minor post activation does occur.

These and other desirable advantages are insured by the instant inventive process which provides a method for producing a nonwoven fabric which comprises intermittently bonding together at least two layers, at least one of said layers comprising individualized nonactivating fibers and at least one other of said layers comprising individualized activating fibers having a fiber length greater than the space between adjacent binder areas, and exposing said bonded fabric, under controlled tension, to a temperature of from about 35 0 F. to about 400 F for at least about one second, to provide a heat-set fabric characterized by substantially uniform ripples of predetermined magnitude.

The temperature range recited above is restrictive in that it defines the thermosetting temperature range, i.e., the temperature range wherein the thermosetting characteristics providing no greater than about 2% post activation are imparted. Activation of the activating fibers providing buckles or ripples will result within a broader temperature range of from about 200 F. to about 400 "5.; therefore, activation alone can occur without the thermosetting range or can be accomplished in a separate process step with the process of the instant invention following at some later interval of time.

The phrase under controlled tension is used herein to characterize the state of the fabric substantially immediately before and after it is subjected to a heat source providing a thermosetting temperature of from about 350 F. to about 400 P. which activates specific fibers and insures the definitive rippling or buckling in the fabric. The fabric is permitted a predetermined amount of freedom or slack just prior to its treatment with this heat, so that it will be allowed to decrease or shrink essentially in its lengthwise direction, an amount approximately equal only to the extent of the slack provided. This given or predetermined amount of decrease or shrinking is insured by the provision of controlled restriction or ten- 3,485,699 Patented Dec. 23, 1969 sion on the fabric substantially immediately afer the given activation of specific fibers by heat. This makes certain that only the given slack is taken up in the activation of the fabric and that the activated fabric itself is not pulled back after passing through heat treatment to increase the extent of activation beyond that which was desired or predetermined. This will be more clearly understood by later reference to FIGS. 3-6 of the drawings.

The amount of slack or freedom which is to be given to the fabric prior to activation to insure a specified percent of shrinkage or activation in the fabric is determined by the amount of activation permitted by the activating fibers, as well as by the rate at which the fabric is permitted to pass the heat source and the rate at which it is taken up after passing the heat source, i.e., after activation.

Certain fibers can only shrink a given amount, therefore, inherent limitations are provided, e.g., Rhovyl fibers (polyvinyl chloride fibers manufactured by Societe Rhovyl), can shrink only up to about 60% of their original length. However, governed only by these inherent limitations, these fibers can be made to shrink a predetermined amount by utilizing both the given thermoplastic temperature range and controlled tension of this invention.

The controlled tension provides the means whereby the amplitude of the buckles or ripples in the fabric can be predetermined, since the allowance of a given amount of slack, or fabric free of tension prior to heat treatment, and the provision of a given tension on the fabric after the heat setting treatment insures that only the slack provided can be taken up during the activating process. For example, utilizing Rhovyl fibers as the activating fibers and providing slack of 40% prior to the application of the thermoplastic temperature will insure a shrinkage of 40% in a fabric utilizing these fibers and made in accordance with this invention.

The controlled tension also insures that the rows of buckles or ripples are of substantially uniform spacing and magnitude throughout the fabric since the tension is supplied uniformly on the fabric during the thermosetting treatment. That is to say, that the buckles will have substantially the same amplitudes throughout the fabric ant the distance between the rows of ripples will be substantially equal throughout the fabric as long as the tension provided remains consistently uniform.

More particularly, the instant invention provides a process for preparing a nonwoven fabric having three-dimensional surface interest which comprises bonding together a plurality of webs of individualized textile fibers in a predetermined pattern of spaced binder areas, at least one of said layers comprising a fibrous web of nonactivating fibers and at least one other of said webs comprising a fibrous layer of activating fibers having a fiber length greater than the space between adpacent binder areas, exposing said fabric, under controlled tension to a thermosetting temperature of from about 350 F. to about 400 F. for about at least one second to provide a fabric characterized by a series of substantially uniformly buckled sections and concomitant trough sections, said trough sections representing the binder areas wherein said fibers are closely associated in substantially the plane of the fabric, and said buckled sections being of predetermined amplitude wherein the individual fibers are substantially diffused with respect to one another between the plane of the fabric and the vertex of said buckled section.

As used herein the phrase plane of the fabric refers to a plane running laterally through approximately the lowest portion of the base of each of the cavities forming the troughs or binder areas of the fabric. Thus, the plane of each fabric would connect the approximate points, L, of

3 each trough portion of the fabric as is shown in each of the FIGURES through 6.

The term percentage shrinkage as used herein is defined-as equaling the original lentgh of the fabric minus the shrunken length of the fabric after the desired shrinking has been developed, divided by the original length 0 the fabric, all taken times 100.

By the term differential in shrinking as used herein is meant the measurable difference in the llevelopment of the shrinking properties of one type fiber as compared to that of another type. One of the factors effecting differential in shrinking is temperature. To explain, the shrinking properties of the fibers of one type or kind would be developed at a given temperature or within a narrow temperature range, while the shrinking properties of another type or kind of fiber, (1) may be developed to a measurable, but to very much lesser, extent at that temperature, or (2) may not be developed at that temperature even though the fiber has latent shrinking properties, or (3) is not developed because that particular fiber does not have shrinking properties.

In light of the preceding discussion, it is understood that the fibers that shrink at the lower temperature to an extent sufficient to be directly, and essentially solely, responsible for the characteristic buckling of the fabric are termed the activating fibers, While the remainder are termed nonactivating fibers, even though the latter may fall into categories (1) or (2) as defined in the preceding paragraph. Thus in the case of heat treatment, the fibers which have their shrinking properties developed at the lower temperature and thus affect the buckling, are the activating fibers. The treatment temperature is then dependent upon the known temperature at which the shrinking property of the fibers is developed. In the case of other means of activation, e.g., chemical, it is that known condition, state or reaction which developes the shrinking properties of one type or kind of fiber, i.e., activating fibers, without affecting or developing more than a very minor degree, the shrinking properties of any other type or kind of fiber present in the fabric. Therefore, in all cases the characteristic buckling is directly related to, and dependent upon, the extent or degree of shrinkage of the activating fibers.

The treatment applied to the fabric to activate the activating fibers is heat within the range of about 200 F. to 400 F.; however. specific thermosetting heat within the range of from about 350 F. to about 400 F. is necessary to heat-set the fabric and insure that there is less than 2% post activation of these activating fibers. The space from the heat source to the fabric will not substantially effect the magniture of the buckling in the fabric as long as required heat is in the fabric.

With less than about 350 F. there is insufficient heat supplied to effect the heat-set desired and the use of heat above about 400 F. accomplishes no useful, but probably a detrimental, effect. An area of the fabric is to be subjected to this heat for at least about one second to provide heat setting as well as to provide the buckling if they are to be accomplished simultaneously. The duration of exposure, as well as the temperature applied, is controlled by the scorching of the fabric which would result if either of the variables is adjusted to overexpose a given area of the fabric to a temperature of such intensity as to burn or scorch the fabric and thus destroy it. Also, the buckles or ripples, if they are already present prior to this application of the instant process, may be collapsed by application of too much heat to a given area.

The activating fibers of the illustrative heat-shrinkable web may be selected from a large group of fibers having such heat-shrinkable properties. Representative of such fibers are certain types of the following fibers: the vinyl polymer fibers, notably Vinyon, a vinyl chloride-vinyl acetate copolymer composed of at least 85% and usually up to 90% by weight of vinyl chloride; Rhovyl, a polyvinyl chloride polymer; saran, a polyvinylidene chloridevinyl chloride copolymer composed usually of from about 4% to about 15% by weight of vinyl chloride; polyesters such as Dacron and Kodel; polyolefins such as low, medium and high density polyethylenes, isotactic polypropylenes; acrylics and modacrylics such as Dynel, Verel, Acrilan, etc. Such fibers may also be included in the nonactivating web, if desired.

Although a few representative activating or shrinkable fibers have been disclosed, it is to be appreciated that the inventive concept in its broader aspects is not to be construed as limited thereto. Substantially any synthetic thermoplastic fiber may be so manufactured or processed as to possess some shrinkage capabilities and consequently substantially any synthetic fiber may potentially be applicable to the principles herein disclosed. The greater the shrinkage, the greater is the potential application. As an indication of the degree of shrinkage involved, it can be stated that Rhovyl exhibits normal shrinkages up to about 60%; Verel up to about 50%; Dacron up to about 45%; and Dynel up to about 50%. Under controlled temperature conditions, these percentages may be varied upwardly or downwardly. Other fibers containing greater or lesser percentage shrinkages are, of course, useful where such greater or lesser effects are desired.

Within this invention, the activating fibers must shrink to at least about 15% of their original length in order to present a buckled or rippled fabric having the desirable properties.

It is to be noted that the fibers must be in a relaxed condition during the shrinking process so that they are permitted to contract freely within the unbonded areas. If restraint is placed on the shrinkable fibers, i.e., on the fabric as a whole, their degree of shrinkage is accordingly modified and controlled, as desired or required.

The nonactivating fibers may be selected from a large group of fibers which are relatively nonshrinkable with respect to the shrinkable fibers, e.g., heat-shrinkable fibers.

Representative of such nonactivating fibers are the natural fibers, notably, cotton and linen, or the synthetic fibers, notably, the cellulosics such as regenerated cellulose made by the viscose or cuprammonium process, cellulose esters such as the acetate and triacetate; polyamides such as nylon 6/ 6, nylon 6, nylon 11, etc.; fluorocarbons such as Teflon; mineral fibers such as glass, etc.

Inasmuch as the three-dimensional effect is obtained by means of the difference in heat-shrinking properties, it is possible to obtain such an effect by using two heatshrinkable fibers, provided the difference in heat-shrinking properties is sufficient, or if the heat-shrinkable properties of one may be developed without developing the heatshrinkable properties of the other. The important factor to be considered, therefore, is the differential in shrinking which is developed under the conditions to which the webs are exposed during the heat treatment.

It is not essential that each fibrous web be composed of only one type of fiber. Blends and mixtures are, of course, possible in the nonshrinkable web as well as in the shrinkable web. However, it must be remembered that the blends or mixtures of fibers be such that the desired heat-shrinkable properties be developed. For example, in the case of the heat-shrinkable web, per se, it has been found that as little as about 12% by weight of activating fibers, of the total weight of the combined Webs that represent the fabric, may be present therein and still develop sufficient heat shrinkability.

The percentage of the activating fibers with respect to the total weight of all the webs in the nonwoven fabric is also a factor to be considered to insure the development of the desired surface effects. As little as about 12% by weight of the activating fibers on an over-all basis has been found satisfactory; although from about 16% to about 50% by weight is found preferable. Greater than 50% by weight may be used where special effects are desired.

It is possible that one web of substantial thickness can be utilized provided that at least 15% of the total weight of that Web contain activating fibers dispersed substantially uniformly throughout. The resultant web can be bonded and activated to produce an acceptable buckled fabric and, of course, the process of this invention can be practiced either in combination with the activation procedure or separately.

It is preferred that the individualized textile fibers be of textile staple or equivalent length, or at least cardable, that is to say, from about /2 inch in average length up to about 3 inches or more in average length. Shorter fibers, down to about inch average length or even of lesser length may be added in various proportions to comprise up to about by weight of the web.

It is essential that the length of the activating fibers, regardless of the web forming process used, must be sufficiently great as to bridge the gap between the two adjacent binder areas. In this way, substantially all of the shrinkable fibers are bonded in at least two points along their length, in order that they satisfactorily transmit buckling or pufiing stresses to the unshrinkable fibers. The lengths of these shrinkable fibers must therefore be greater than the interbinder spaces and normally are at least 1 /2 and preferably at least 2 times the interbinder space. The particular interbinder space used will depend upon many factors such as the binder areas selected, the binder itself, the use of the bonded fabric, etc. For specific values of such interbinder spaces, reference is made to the specific binder patterns noted in the U.S. patents referred to herein and U.S. Patent 3,009,822 to Drelich et al.

The interbinder space will also depend to a considerable extent upon the percent binder coverage of the nonwoven fabric, inasmuch as the greater the percent binder coverage, the less the interbinder space will tend to be. In a preceding paragraph, mention was made that the total surface coverage of the binder areas or lines should not desirably exceed about 35% of the total surface of the nonwoven fabric. Such, however, is not intended to preclude the application of the present inventive concept to nonwoven fabrics wherein the binder coverage is substantially greater than about 35%. Normally, the greater the binder surface coverage, the less dramatic is the surface interest which is developed. Nevertheless, in some uses, such lesser surface interest is desired or required. The individual binder pattern areas or lines may therefore be increased in size or thickness, or there may be a greater number of binder pattern areas or lines per unit area, or a binder may be employed which migrates or spreads on the nonwoven fabric after being applied to thus cover a greater percentage of the surface area, say, up to or coverage. It is to be kept in mind, however, that there still remain interbinder spaces in which there is either no binder material at all or such small amounts of binner material that the free action of the fibers bridging the gap between the two adjacent binder areas is not hampered or impeded.

The denier of the synthetic fibers used in forming the Webs is preferably in the range of th approximate thickness of the natural fibers mentioned and consequently deniers in the range of from about 1 to about 3 are preferred. However, where greater opacity or greater covering power is desired, deniers of down to about or even about /2 may be employed. Where desired, deniers of up to 10, 15, or higher, may be used. The minimum and maximum denier are, of course, dictated by the desires or requirements for producing a particular web or nonwoven fabric, and by the machines and methods for producing the same.

The weight of the individual fibrous web or layer of starting material may be varied within relatively wide limits, depending upon the requirements of the finished product. A single, thin web of fibers, such as produced by a card, may have a weight of from about 40 to about 200 grains per square yard. The minimum weight of nonwoven fabric contemplated by the present invention is, however, about grains per square yard, obtained by plying three webs. The maximum weight may range upwards to about 3000 grains or more per square yard. Within the more commercial aspects of the present invention, however, Web weights of from about grains per square yard to about 2000 grains per square yard are contemplated. These weights are measured prior to shrinking of the fabric and will increase subsequent to shrinking.

The number of layers of webs in the starting materials must, of course, be at least two, in order to obtain the desired or required effects. Three, four, five or more layers, in any desired arrangement may be used where special effects are desired.

The binder used in adhering the plurality of webs together may be selected from a large group of such binders known to industry. It is necessary, however, that a binder be used which can satisfactorily adhere to and bond the different types of fibers together. The binder chosen must bind the shrinking or activating fibers at the binder areas and not just the nonactivating fibers.

Representative of the binders available for such a purpose are: regenerated cellulose; vinyl resins such as plasticized or unplasticized polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, etc., either as homopolymers or copolymers; acrylic resins such as ethyl acrylate, methyl methacrylate, methyl acrylate, butyl methacrylate, etc.; butadiene resins such as butadiene-acrylonitrile, butadienestyrene, etc.; other synthetic rubbers; natural rubber; urea resins such as ureaformaldehyde, cyclic urea-formaldehyde, etc.; aldehyde resins such as melamine-formaldehyde, phenol-formaldehyde, res0rcinol-formaldehyde, etc.; epoxy resins; cellulose derivatives such as carboxymethyl cellulose; hydroxyethyl cellulose, etc.; starches, gums; casein; etc.

The binders may be added, as desired, in the form of emulsions, solutions, dispersions, plastisols, powders, etc. Autogenic bonding, preferably by heat and/or pressure and/or solvents, may also be used when thermoplastic fibers are present.

The percent add-on of such binder materials may be varied within relatively wide limits, depending to a large extent upon the specific binder employed and upon the type, weight and thickness of the nonwoven fabric. For some binders, as low as about 1% by weight up to about 12% by weight, based on the weight of the dry webs being bonded, has been found satisfactory. For other binders, as high as from about 15% to about 50% by weight has been found preferable. Within the more commercial aspects of the present invention, however, from about 2% to about 35% by weight based on the Weight of the dry webs being bonded has been found desirable.

The particular size, shape and configuration of the binder pattern used falls Within the scope and range of binder areas previously used in the prior art. Examples of some of these binder patterns may b found in the above-mentioned U.S. Patents 2,705,687 and 2,705,688 or in U.S. Patent 2,880,111. Specific examples of binder areas, binder shapes and sizes, and interbinder spaces are noted in said patents.

After the binder material has been applied to the fibrous web and set, either by regenerating, curing, heating, or drying, the bonded fibrous web is passed in a relatively relaxed condition to permit shrinkage over internallyheated speed-controlled drying cans or through a heated oven maintained at a temperature sufficiently high to activate and shrink the heat-shrinkable fibers. Overfeeding may be resorted to in order to provide the desired slack for shrinking or to control the extent of the shrinking. Other things being equal, it has been found that the exposure time may be decreased by using a higher temperature, and that a lower temperature may be used in some caess to avoid fiber damage by using increased exposure periods. Subsequent to the development of the heat-shrinkable properties, the three-dimensional nonwoven fabric is forwarded for further processing as desired or required. Of course, the drying temperature for the binder chosen must be less than that necessary for development of the activating fibers since the binder areas must be firmly established and must firmly contain the fibers or else slippage which Would destroy the buckles will be in evidence.

In some instances it is desired that the activating fibers shrink in the fabric to a greater degree than is permissible under the techniques and times permitted for commercialization; however, it has been found that if the moisture in the fabric is controlled during activation such that the moisture content is from about 15% to about 20% by weight, based on the dry fabric Weight, maximum buckling of the fabric, i.e., maximum shrinking in the activating fibers, is developed. Below about 15% there is no appreciable effect on the degree of buckling or activation, while above abgit 20% there is no significant activation of the fibers in the fabric because there is too much moisture. This moisture may be provided by using steam as the heat source. As was the case with the thermosetting heat source, the distance from the fabric of the moisture source is important only in that it provide the required moisture in the fabric at the time of heat setting. Not only is maximum shrinkage or activation attained using the above teachings but maximum activation is attained within relatively the same time as it takes to promote the aforedescribed activation absent this specified moisture.

The inventive concept will be described in greater specificity by reference to the accompanying drawings and following specification wherein there is illustrated and described preferred embodiments of this invention. It must be understood, however, that the inventive concept is not to be considered limited to the embodiments described except as determined by the scope of the appended claims. In the drawings:

FIGURES 1 and 2 depict schematically the process of the instant invention and specific apparatus which could be utilized.

FIGURE 3 is a plan view of a fabric processed in accordance with the instant invention.

FIGURES 46 are cross-sectional photomicrographs taken along the length of adjacent buckles made in a fabric in accordance with this invention.

In FIGURE 1 there is illustrated apparatus suitable for carrying out the principles of the present inventive concept. The nonwoven fabric is composed of a web 2 comprising non-heat-shrin'kable fibers, upon which is positioned a second web 3 comprising heat-shrinkable fibers and a third web 4 comprising non-heatshrinkable fibers.

The three webs, 2, 3 and 4 are bonded together with a spaced intermittent bonding line pattern by being passed through the nip of a backing roll 5 and an applicator line-printing roll 6 which is in contact with an immersion roll 7 in a binder bath 8. The rolls 5, 6 and 7 are so adjusted that the binder agent is picked up from the binder bath 8 by the immersion roll 7, transferred to the applicator roll 6 and pressed into the nonwoven fabric 1 in intermittent lines by means of the backing roll 5.

The binder is then set by being regenerated, cured, heated or dried, as desired or required for the particular binder involved, in a setting unit 9 and the bonded nonwoven fabric is then heat-treated in accordance with this invention and taken up on supply roll 20.

FIGURE 2 depicts schematically one embodiment of the method of this invention. The fabric 1 of FIGURE 1 is taken from supply roll 20 and is passed over a first set of rolls 21a and 21b which are the first pair of the set of four cooperating tension rolls. The fabric 1 is then subjected to a heat source 23 and through a second pair of cooperating tension rolls 24a and 24b. The uniformly buckled and heat-set fabric is then taken up on roll 25. Basically, the speed of the fabric being fed to the heat source 23 by rolls 21a and 21b, minus the speed of the fabric being taken up at rolls 24a and 24b, divided by the speed of the fabric being fed in by rolls 21a and 2111, all taken times 100, provides the percent shrinkage that is uniformly being imparted to the fabric. It can readily be understood then that consistent with the allowable shrinkage in the fabric, the amount of shrinkage can be predetermined by regulating the respective speeds of feed-in and take-up of fabric 1 or specifically, in this instance, by regulating the revolutions per minute of rolls 21a and 21b as well as 24a and 24b. Rolls 21a and 21b will be rotating or revolving faster than rolls 24a and 24b since only by such an arrangement can slack be provided in the fabric prior to heat treatment and resultant activation. The fabric 1 between the two sets of cooperating rolls 21a, 2111' and 24a, 24b must be free of restrictions which will interfere with the activation and the resultant shrinkage in the fabric 1. Thus it should not be carried by a belt if the belt provides resistance in the fabric which would counteract the effect of the slack provided, nor must the distance between the pairs of cooperating rolls be too great. Should maximum uniform buckling of the fabric be desired, a source of moisture 26 can be positioned prior to heat treatment in order to impart the required 15 to 20% of moisture in the fabric 1 to insure maximum activation, consistent with the inherent limitations in the fabric. Of course, this could also be accomplished by uitilizing steam as the means of activation and by controlling either the distance between the fabric and the source of steam or the amount of moisture in the steam to insure that only the desired moisture be imparted to the fabric.

Absent the controlled tension applied to the fabric, the activation of the fabric would be the maximum permitted by the fabric consistent with the procedures utilized and uniform buckling could not :be anticipated.

The heat imparted by the heat source can be radiant heat supplied in accordance with known procedures or any other source of heat known and utilized by the textile art under similar conditions.

It is to be understood that the process of this invention need not be separated by the procedure of having the fabric 1 taken up on supply roll 20 prior to activation. The fabric 1 could be passed into the heat under controlled tension after curing of the binder and a continuous process would be established.

FIGURE 3 is a photomicrograph of 4 magnification of a plan view of a fabric containing layers of activating and nonactivating fibers. The fabric is constructed following the teachings of U.S. 2,862,251 which provides the plurality openings defined =by bundled fibers, and it is then processed in accordance with the instant invention. A wavy-line pattern has been used to bond the fibers of the fabric and is in evidence by the corresponding wavy-line pattern of each row R of buckled fibers. The troughs or binder areas are represented by the areas designated T. Note should be taken of the fact that even though the binder is applied via a Wavy-line pattern and the buckles or ripples in each of the rows R do conform the wavy-line pattern of the binder areas T, the distance between rows R remain substantially constant between each of any of two adjacent rows and, in fact, throughout the fabric. It should also be noted that each of the rows R appear to be defined by buckles of substantially equal magnitude and that each of the rows run uninterruptedly, i.e., without areas along their length which are devoid of buckles or without evidence of termination along their lengths.

FIGURES 4 through 6 are cross-sections taken at A1 inch intervals along the same three rows, i.e., R1, R2, R3, of buckles. Note should be taken of the fact that the magnitude of a buckle in any one of these rows does not vary substantially although the buckle may sag a trifle to one side, and that the distance between buckles along any row remains substantially constant throughout. This is due to the uniform rippling which is brought about by this invention. As a result, the properties of the fabric are uniform throughout and the properties of the fabric are, therefore, of predictable consistency which defines a dependable fabric. The degree of the presence of the properties of the fabric that are brought into being by these adjacent rows of buckles may be increased or decreased as desired since the amount of buckling is controlled by the process of this invention. This would include absorbency, bulk, softness and hand to mention a few.

From the above photomicrographs it can be seen that controlled shrinkage causes the more shrinkable of the fibers, not in the print or bonded areas, to contract, causing the nonactivating fibers to buckle in a predetermined uniform amount and intermingle somewhat depending upon the weight of the fabric as a whole, the number and individual weight of the initial starting layers; as well as the degree and type of print bonding employed, and the percent shrink and the length of the fibers involved. For example, if the initial fabric were to be print bonded on both sides using two different print patterns, one on each side, an out-of-phase series of bicorporal buckles would certainly result. This could be employed to a point where the individual buckles projecting from opposed sides of the fabric could not be termed bicorporal since the base of one might more nearly approach a contiguous relationship to the base of a trough separating two ripples which project from the other face of the fabric.

Under activating treatment, i.e., shrinking treatment, the activating fibers within the unbonded areas, that are bonded along their length at points in adjacent bond areas and therefore span an unbonded area, contract. Those activating fibers that do not span that individual unbonded area even though these fibers are also bonded twice along their length and are of a length sufiicient to span the bond zone, contract and buckle or extend away from the palne of the fabric. The contraction of the activatinng fibers that span an individual unbonded area and are therefore bonded along their length in each of these bond areas, forces the nonactivating fibers to buckle and extend away from the plane of the fabric L. Thus, dispersed between the plane of the fabric L and the vertices of the buckles are a mixture of activating and nonactivating fibers, while running along the plane of the fabric are those activating fibers that are firmly seated in the adjacent bond areas and span the unbonded areas. These latter activating fibers are directly responsible for the buckling which effects a diffusion of fibers in the unbonded areas. The fibers within the buckle are diffused with respect to the position they occupied in the laminate prior to shrinkage of the fabric, and while the majority of both the activating and non-activating fibers, in the nonbonded areas, follow the contour of the buckle, many become intermingled to extend throughout the interior of the buckle to provide varying fiber density between the plane of the fabric and the vertex or vertices of the buckle.

Within the bonded areas there is very little, if any, contraction by the activating fibers during activating or shrinkage treatment since all fibers within each of these particular areas are held by the binder and they thus remain in their closely associated relationship. Thus in the bond areas there are no interfaces defining the individual webs or layers and the individualized fibers of one layer grade into those fibers of the other layer to provide a diffused zone betwen webs wherein the fibers of both webs are intermingled and entangled and wherein the entire bond zone is represented by fibers that have been compressed to close fiber association by the application of the webs one to another and by application of the binder.

The buckles, ripples, or pillows become permanent in nature since the activating fibers are bonded at least twice along their length, and because those that span an individual unbonded area are firmly seated in adjacent bonded areas. Thus when these particular activat- 10 ing fibers are made to contract, they can not be destroyed without breaking at least one of the two bond sites on each of these activating fibers that span the unbonded areas.

The fibers within the buckles are diffused and within any particular cross-section, which merely represents a plane bisecting the fabric, the fibers are diffused between the plane of the fabric and the vertex of the buckle. The extent or degree of diffusion varies with the type of bond, the extent of shrinkage, etc., as was discussed earlier. However, the buckles or ripples extend, in length, beyond this one cross-sectional plane, a distance which is regulated by the print pattern and the type of print.

A fuller description of a similar fabric is given in the earlier identified US. Patent 3,214,323; however, it is to be realized that the buckles or ripples may extend away from one surface of the fabric or from two surfaces dependent on the construction of the fabric, i.e., the positioning and the number of webs of activating and nonactivating fibers. Additionally, the rippling may take place in one direction or in two opposed directions in internal structure of the fabric where the buckles will not be seen on the surface of the fabric as a whole. This again would depend on construction, i.e., the positioning and the number of webs of activating and nonactivating fibers which are laminated or bonded together to form the fabric.

The invention will be further illustrated in greater detail by the following specific examples. It should be understood, however, that although these examples may describe in particular detail some of the more specific features of the invention, they are given primarily for purposes of illustration and the invention in its broader at pects is not to be construed as limited thereto.

EXAMPLE I A card web weighing 180 grains per square yard and comprising 50% by weight of 1 /2 denier, 2-inch staple length viscose rayon and 50% by weight of cotton is plied with a second card web weighing 180 grains per square yard and comprising 50% by Weight of 1 /2 denier, 2-inch staple length viscose rayon and 50% by weight of 1.8 denier, 2-inch staple length Rhovyl 55 fibers (heatshrinkable polyvinyl chloride fibers made by Societe Rhovyl). The plied Webs are print bonded with a wavyline print pattern extending across the width thereof basically at to the long axis of the webs. There are four wavy binder lines per inch of fabric, with each wavy binder line measuring about 0.006 inch deep x 0.018 inch wide. The binder used is a combination thermosetting-thermoplastic resin comprising melamine-formaldehyde and Rhoplex B-l5 (an ethyl acrylate resin binder made by Rohm & Haas). The percent binder addon is about 20% by weight, based on the weight of the nonwoven fabric. The surface coverage is about 24%. The binder is dried at about 230 F.

The bonded web is let off over a steam manifold and fed into a first pair of cooperating rolls operating at a linear speed of 50 yards per minute. The steam manifold is adjusted so as to impart 15% moisture to the fabric based on the dry fabric weight. A second set of cooperating rolls were discharge rolls and are set to operate at 25 yards per minute.

The heat source is a bank of electric-powered infrared heaters positioned away from the fabric a distance such that the fabric passing beneath the units at the preset rate is raised to a temperature of 380 F.

The fabric shrinks 50% and is heat-set and is discharged and rolled up at 25 yards per minute. The fabric has approximately 6 ripples per inch.

A sample of the rippled, heat-set fabric is placed in a steam sterilizer and subjected to wet steam at 2500 F. for 20 minutes. Upon removal from the sterilizer, the fabric is found to have undergone additional shrinkage of less than 1%.

The weight of the bonded nonwoven fabric prior to the heat treatment is about 430 grains per square yard. Subsequent to heating, the fabric weighs about 650 grains per square yard. Such a fabric is suitable for use as a disposable face towel. It is soft, bulky and lofty and possesses increased absorbency due to the increased rip pled surface area. It has an excellent appearance and an unusual rippled surface interest.

EAMPLE II A six-layered fibrous structure is prepared as follows: each of the interior layers, i.e., layers 3 and 4, are carded and consist of 60% by weight 3.0 denier, 1 /2 inch staple Rhovyl 55 and 40% by weight SN5813 surgical rayon. The four outer layers, i.e., layers 1, 2, 5 and 6, are also carded and are composed of 100% |SN5813 surgical rayon. Following the procedure taught in US. 2,862,251, the laminate of six Webs of loosely assembled fibers is fed into fiber rearranging apparatus, and 95 holes per square inch (staggered) are provided therein. The plied laminate is then print bonded with a wavy-line print pattern extending across the width thereof basically at 90 to the long axis of the webs. There are 4 wavy binder lines per inch of fabric, with each wavy binder line measuring about 0.024 inch wide. The binder used is viscose.

The procedure of Example I is followed with the feed rolls operating at 30 yards per minute and the discharge rolls at 24 yards per minute. Moisture is added via the steam atmosphere to 20% based on the dry fabric weight. The heat source is operated to yield the same temperature conditions of Example I in the fabric. The fabric shrinks 20%. On subsequent testing in the sterilizer, it is found to have less than 1% residual shrinkage.

EXAMPLE III Using the fabric of Example I, the material is subjected to the same rippling conditions as described except the feed or first cooperating roll nip is eliminated and the fabric is only allowed to reach a temperature of 280 F. With only the second set of cooperating rolls in effect, the fabric is allowed to shrink to maximum under no control. Since the temperature obtained is only 280 F., the fabric will ripple but will not be heat-set. The resultant fabric, because of the uncontrolled tension at the time of shrinkage, is unevenly rippled and when subsequently steam-sterilized, it shrinks another 8%, making it undesirable for surgical applications.

This fabric is used as a disposable surgical sponge and these sponges are usually wet in saline solution and then rung out prior to use where they function to pack body cavities and to protect vital organs in operational procedures. Prior to buckling or rippling by heat treatment, the fabric measured 18 x 18 inches and weighed 950 grains per square yard. After buckling (heat treatment) the fabric measured 18 x 15% inches and weighed 1250 grains per square yard.

The bonding operation employed for stabilizing and strengthening nonwoven fabrics has taken on many forms, one popular form being the intermittent bonding of the nonwoven fabric with a predetermined pattern of spaced, discrete binder areas or lines extending across the width of the nonwoven fabric. The individual fibers passing through these binder areas or lines are adhered into a stable, self-sustaining relationship. The binder areas may also take on any desired shape or form including circles, annuli, ovals, ellipses, triangles, rectangles, squares, diamonds, parallelograms, or other polygons, 0r combinations of such forms either regularly or irregularly shaped. The binder lines may extend across the nonwoven fabric at any desired angle to the long axis; the binder lines may be parallel, or they may cross each other to form diamond or irregular polygonic figures; the binder lines may be continuous or discontinuous; or they may be straight, curved, sinuous, or irregularly wavy. Examples of some of these 12 patterns and shapes may be found in the above-mentioned US. Patents 2,705,687 and 2,705,688 or in US. Patent 2,880,111.

One common factor, however, is to be particularly noted in all of these patterns, namely, that the total surface coverage of the binder areas or lines on the nonwoven fabric should not substantially exceed about 35% of the total surface of the nonwoven fabric. Preferably, such coverage should be less than about 25% and sometimes down to about 8% of the total surface of the nonwoven fabric. Fabric made in accordance with this invention may be used as wrapping and packaging materials, surgical dressings, sponges and bandages, covers or other components of sanitary napkins, hospital caps, dental bibs, eye pads, dress shields, diapers and diaper liners, casket liners, wash cloths, hand and face towels, handkerchiefs, table cloths and napkins, curtains and draperies, quilting or padding, cleaning materials, shoe shine cloths, battery separators, etc. Because of this wide variety of uses, these nonwoven fabrics are available commercially in a wide range of fabric weights of from as little as about grains per square yard to as much as about 2600 or more grains per square yard.

Although several specific examples and embodiments of the inventive concept have been described, the same should not be construed as limited thereby nor to the specific substances or constructions mentioned therein but to include various other equivalent substances and constructions as set forth in the claims appended hereto. Weights, dimensions and other physical properties referred to herein refer to the fibrous Webs or nonwoven fabrics, prior to the heat-shrinking process, unless specifically stated otherwise. It is understood that many changes, modifications and variations may be made without departing from the spirit and scope of the invention and that the invention is to be limited only by the appended claims.

What is claimed is:

1. The method for preparing a nonwoven fabric having buckles and troughs creating a three-dimensional surface interest and exhibiting less than about 2% post-activation shrinkage when exposed to a temperature of up to about 350 F. which comprises:

(1) bonding together at least two webs of individualized textile fibers in a predetermined pattern of spaced binder areas, at least one of said webs comprising non-activating, relatively non-heat-shrinkable fibers and at least one other of said webs comprising heat shrinkable activating fibers, said non-activating fibers and said activating fibers having a fiber length greater than the space between adjacent binder areas;

(2) feeding said bonded webs into a heating zone having a temperature of from about 200 F. to about 400 R;

(3a) exposing said bonded webs in said heating zone initially to an activating temperature of from about 200 F. to about 400 F. tending to cause maximum shrinkage of said heat shrinkable activating fibers and to create buckled sections and trough sections in said bonded webs;

(3b) exposing said bonded Webs in said heating zone finally to a heat setting temperature of from about 350 F. to about 400 F., causing said buckled sections and trough sections to become heat set in the shrunken condition they attain during exposure to said activating temperature whereby they exhibit less than about 2% post activation shrinkage when exposed subsequently to temperatures of up to about 350 F., and

(4) restraining said heat Shrinkable activating fibers during said exposure to said activating and heat setting temperatures in said heating zone whereby said heat shrinkable activating fibers are placed under controlled tension and attain a predetermined shrinkage less than maximum shrinkage, said restraining of said heat shrinkable activating fibers being accomplished by Withdrawing said bonded webs from said heating zone at a rate insufficient to permit maximum shrinkage of said heat shrinkable activating fibers.

2. The method described in claim 1 wherein the bonded nonwoven Webs are pretreated With moisture prior to being fed into the heating zone to bring the moisture content into the range of from about 15% to about 20%.

3. The method described in claim 2 wherein the moisture is provided by a pretreatment with steam.

4. The method described in claim 1 wherein the activating fibers comprise polyvinyl chloride fibers and the activating temperature is less than about 280 F. at which temperature activation of the polyvinyl chloride fibers takes place but at which temperature substantially no heat setting of the polyvinyl chloride fibers takes place.

References Cited UNITED STATES PATENTS 3/1950 Lannan 156-474 3/1959 Drelich 161148 XR 10/1965 Russell et al 161-148 US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, +85,699 Dated December 23, 1969 Inventor) A Lton H. Bassott and Charles H. Plwnmer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F- In the references cited, the Lannan patent number should read "2,500,690" instead of 2,500,069

SIGNED AN SEALED MAY 121970 I Anew Edward M. Fletcher, 11'. 1:. 50m JR.

Attesting Officer Commissioner of Patent: 

